It is desirable to reduce the weight of glazing used in automotive vehicles. At present four main types of automotive glazing are of interest for weight reduction: (1) overall reduced thickness of the glass, (2) bi-layer laminated glass/plastic sheet, (3) plastic sheets with hard and scratch resistant coating, (4) multi-layer glass/plastic glazing. Weight reduction by reduced overall glass thickness is limited, however, because of manufacturing, noise and security requirements: The glass pane must be manageable during the whole manufacturing process. The manufacturing process for laminated windshields disclosed in EP 0 245 175 B1 will allow only slight reduction in thickness. Furthermore thickness reduction will increase the interior noise level because thinner glass transforms windnoise as well as body vibrations more directly to the interior. That means also sidelites, mostly affected by windnoise, are limited with regard to thickness reduction. In addition, all glazing must meet security requirements which requires a certain thickness of glazing all around the vehicle.
The main disadvantage of glazing made from bi-layer sheets of glass and plastic is the less than desirable scratch resistance of the plastic surface, which is not satisfying for automotive applications at the moment. Lightweight glazing could also be achieved by manufacturing the glazing from plastic sheets, covered with scratch resistant surfaces. Several disclosures deal with this approach, but at the moment none of these technologies has been introduced on high volume products.
A very efficient approach for lightweight glazing is a "Sandwich" glazing, i.e., a multi-layer sheet as disclosed in U.S. Pat. No. 5,589,272: Two thin glass layers, one inner and one outer, combined with a thick middle layer made of plastic. Its disadvantage at the moment is the manufacturing process. Handling of the thin glass layers is very difficult, which means that the size of sheets is limited, especially for curved panes.
Therefore, it is a primary object of the present invention to provide a method of manufacturing lightweight automotive glazing based on the Sandwich approach with multi-layer sheets with none of the above mentioned drawbacks. The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken into conjunction with the accompanying drawings.